Field of the Invention
The invention relates generally to the art of air-ride axle suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, and utility trucks, which cushion the ride and stabilize the vehicle during operation. More specifically, the invention relates to a pneumatic control system that is utilized in conjunction with a height control valve for a heavy-duty vehicle air-ride axle/suspension system, which includes an air lock/retention function that maintains a volume of air in the air springs during certain operations, such as an outrigger deployment/retraction operation for a utility truck or placement of a trailer onto a rail flatbed, that would otherwise typically cause the air springs to become completely extended and/or exhausted.
Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, fire/rescue, and utility vehicles, such as landscape, boom trucks, and the like, may include air-ride axle/suspension systems, which use air springs to cushion the ride of the vehicle. Pneumatic control of these air springs is an important feature of air-ride axle/suspension systems.
Heavy-duty vehicles utilize air-ride axle/suspension systems to reduce the possibility of damage to and extend the service life of the truck and the components of the truck, such as hydraulic components, electric components and the fabricated bodies of the truck. More specifically, air-ride axle/suspension systems provide a smoother ride to the vehicle thereby reducing vibrations imparted to the hydraulic components, electronic components, and fabricated body of the vehicle during operation, resulting in reduced potential for damage to the components and increased component life.
More particularly, it is important for a cushioned vehicle ride, and for optimum axle/suspension system performance and longevity, to attempt to maintain a consistent, predetermined distance between the vehicle frame and the travel surface. This predetermined distance is known in the art as the design ride height of a vehicle. The operating conditions of the vehicle must be considered in order to establish the design ride height of a vehicle. That is, when a heavy-duty vehicle executes certain maneuvers, such as making a hard turn or traveling over rough terrain, the forces imposed on the axle/suspension system by such maneuver cause the axle/suspension system to articulate, or pivot and/or flex beneath the vehicle frame which the system supports. Typically, an axle/suspension system is designed so that the anticipated range of articulation, pivoting and/or flexing occurs about a nominal predetermined position, and that nominal position is set as the design ride height of the vehicle.
When a heavy-duty vehicle, such as the trailer of a semi-trailer, is loaded, the air springs are adjusted to ensure that the vehicle is at design ride height while traveling. The pneumatic control or adjustment of the air springs of the axle/suspension system is typically accomplished by a height control valve or leveling valve which is in fluid communication with an air source and with the air springs. When the heavy-duty vehicle is loaded with freight and the air springs of an axle/suspension system are compressed causing the vehicle frame to be positioned below design ride height or closer to the travel surface, compressed air is supplied to the air springs thereby inflating/extending them and, in turn, causing the axle/suspension system to raise the vehicle frame to the design ride height. Conversely, when the vehicle is unloaded and the air springs of the axle/suspension system are extended causing the vehicle frame to be positioned above design ride height or further away from the travel surface, air is exhausted from the air springs reducing the internal pressure of the air springs, thereby deflating/compressing them until the axle/suspension system lowers the vehicle frame to the design ride height. As set forth above, the adjustment of the air springs, including regulation of airflow into the air springs and the exhaustion of air from the air springs, is controlled by a mechanically operated valve known in the art as a height control valve. Adjustments to the height control valve and the linkage that controls activation of the height control valve enable the design ride height to be achieved before the vehicle travels.
As the vehicle travels and the driver executes maneuvers that cause the axle/suspension system to articulate between a position that compresses the air springs and a position that extends them, the height control valve automatically acts to maintain the design ride height. That is, when the air springs are compressed, the height control valve causes air to be supplied to the air springs from a vehicle air reservoir or air tank. Conversely, when the air springs are in an extended position, the height control valve causes air to be exhausted from the air springs to atmosphere. The amount of air that is supplied or exhausted to and from the air springs by the height control valve is based on the duration of the articulation of the suspension beam and the flow rate of the height control valve at a given position.
Certain operating events can cause the axle/suspension system of the vehicle to become completely extended, resulting in complete exhaustion and/or deflation of the air spring by the height control valve. Two such events are commonly known in the industry. The first event occurs when a trailer of a tractor-trailer having an air-ride axle/suspension system is lifted by a crane onto a flatbed rail car. When this occurs, the air springs of the axle/suspension system of the trailer become completely extended as the trailer is lifted off of the ground and the tires lose contact with the travel surface. The second commonly known event occurs when a utility truck having outriggers, such as a landscape truck with a telescopic boom, and having an air-ride axle/suspension system, deploys the outriggers during operation of the vehicle to stabilize the base of the vehicle to prevent rollover. During outrigger operation, the outriggers raise the utility truck until the tires are disengaged from the travel surface, thereby causing complete extension of the air springs of the axle/suspension system. In both events, as the air springs become extended, the height control valve automatically exhausts air from the air springs in order to attempt to return the axle/suspension system to design ride height. However, because the air springs are extended due to an external force, i.e. the outriggers or the crane lifting the trailer off of the ground, exhaustion of the air spring by the height control valve does not return the vehicle to design ride height but rather can potentially create a vacuum in the air bag or flexible member of the air spring, thereby collapsing the air bag inwardly onto itself. When this occurs and when the axle/suspension system is lowered back onto the ground by the outrigger or the crane, the air bag of the air spring can become pinched or trapped between the internal bumper and the upper bead plate of the air spring, resulting in potential damage to the air bag of the air spring. As air pressure is reintroduced into the air springs, the air bag of the air spring can remain pinched, so that when the vehicle encounters a bump, the bag can pop out violently from its pinched state, possibly causing damage to the air bag or air spring piston. In addition, once the air springs have become completely exhausted during one of the lifting maneuvers, it takes longer for the pneumatic control system to re-inflate the air springs in order to return the vehicle to design ride height.
In addition, other operating events can cause increased fore-aft movement of the vehicle, or dock walk. For example, typical trailing beam air suspensions produce dock walk when brakes are applied and suspension travels through jounce and rebound. More specifically, dock walk is defined as fore-aft movement of the chassis caused by the rotation of the tires relative to the ground during suspension travel with brakes locked. Jounce/rebound travel, associated with dock walk, may be caused by mechanical systems, such as outrigger operations, or by air control systems, such as dump valves or overinflate valves. Dock walk can cause high stress on structural components.
Therefore, a need exists in the art for a pneumatic control system that minimizes the possibility of damage to the air bags, or other components, of the air springs by limiting the amount of air or fluid that is exhausted from the air springs during outrigger operations, trailer placement onto a flatbed rail car, and/or other instances when the air springs become completely extended and/or exhausted. Additionally, a need exists in the art for a pneumatic control system that minimizes the fore-aft movement of the vehicle during outrigger retraction operations.
The pneumatic control system of the present invention solves the problems associated with prior art pneumatic control systems by providing a pneumatic control system that locks and/or retains air volume within the air springs during outrigger operation, trailer placement onto a flatbed rail car, or other instances when the air springs of the axle/suspension system of the vehicle are completely extended and/or exhausted during operation and also during outrigger retraction operations.